To the increased background checks.... Might not have helped. If background checks were completely effective, the FBI, CIA and other infiltrated organizations would not have been infiltrated.
On the other hand, if NO background check was/is done, then maybe a elementary check would have helped.
But what are you going to check for?
1. Are you of this religious belief? -- Violation of civil rights
2. Are you from this country? -- Violation of civil rights
3. Do you in tend to harm this country? -- Gotta be a violation of something...
So, unless the applicant is a convicted felon, or has shown radical tendencies (that can be proven without violating civil rights) then there's not much to check for. (Yes, I have had extensive checks done on my background. I'm ex-military with clearances and current job had to have clearances reinstated). What level of background checks are you willing to perform on a "baggage handler"?
And what security would be effective against someone willing to die for his/her beliefs? A bomb, weapon or whatever can be brought in piecemeal and assembled at the work site.
I've listened to the announcers speak of "failed airport security", but I doubt that anyone would accept the imposition required to implement real security. We Americans are too accustomed to our creature comforts and to "speed". "What do you mean stand here in line for an hour for a security check."
Dunno, my take on security. FWIW... my current job is to prepare and test disaster recovery plans. Think anyone believes that there will be a real disaster, "here"?